[29.01] First Helioseismic Results from the Global Oscillation Network Group

J. Toomre (JILA, University of Colorado)

Helioseismology studies the internal structure and dynamics of the sun,
utilizing very precise measurements of the frequencies of sound waves
that propagate throughout the solar interior and are observed at the
surface. Efforts to accurately and precisely measure the mode
frequencies from a single observing site have met with fundamental
limitations imposed by the inevitable interruptions arising from the
day-night cycle. To address such problems, the NSF-sponsored Global
Oscillation Network Group (GONG) project has developed a network of six
identical instruments around the world providing velocity images nearly
continuously, a data processing system that can keep up with the
massive data flow, and is supported by a vigorous scientific community
structured around GONG teams that have shared in all aspects of the
development of the project. Though the primary helioseismic data deals
with the frequencies and their splittings for the nearly half-million
global acoustic modes detectable with the GONG instruments, the data
also allows study of how wave fields are locally influenced by flows
and magnetic structures below the solar surface, and further provides
direct measures of larger-scale flows at the surface.

We shall briefly describe the network, instruments, and data analysis,
and then review some of the preliminary scientific results obtained by
the teams through inversion of the frequency data, dealing with the
structure of the solar interior and the physics of stellar models, and
an assessment of the differential rotation profile with depth and
latitude. Early results will also be presented concerning nearly
steady surface flows of the solar surface.